Measure the existing window opening
Remove the interior trim and exterior stops
Take out the old window sash or frame
Clean the opening and remove old caulk, nails, and debris
Check the opening for damage, rot, or mold
Repair any damaged framing or sheathing
Apply flashing tape and weatherproofing as needed
Dry-fit the new window to confirm the size
Insert the new window into the opening
Shim the window until it is level, plumb, and square
Fasten the window according to the manufacturer’s instructions
Recheck alignment after fastening
Insulate gaps around the frame with foam or backer rod
Seal the exterior perimeter with caulk
Reinstall interior trim and exterior stops
Paint or finish the trim if needed
Test the window to make sure it opens, closes, and locks properly